Reduction of chloride salts in austempering quench baths



Unite States Patent i REDUCTION OF CHLQRIDE SALTS IN AUSTEMPERING QUENCH BATHS John A. Halgren, Downers Grove, and Edward A. Solecki and Robert H. Pinltel, Chicago, Ill., assignors to International Harvester Company, Chicago, 111., a corpora tion of New .lersey Application December 24, 1958, Serial No. 782,830

9 Claims. (Cl. 148-28) bath, used for quenching of steel articles, commonly re- V ferred to as austempering or martempering.

In one process of austem-pering a steel article, the article is immersed in an austenitizing bath of molten alkali metal chlorides at about 1600 F. for a specified period of time. A commonly used commercial chloride austenitizing bath for such purpose may consist of a mixture containing about 50% sodium chloride and about 50% potase siuin chloride. After the immersion time of the article in the fused chloride mixture has elapsed, the article is removed from the chloride austenitizing bath and immediately immersed in an austempering quench bath. The austempering quench bath initially may consist of a mixture of about 20% sodium nitrate, 52% potassium nitrate, and about 28% sodium nitrite maintained at a temperature of about 750 F. After immersion in the austempering quench bath for a specified period of time the article is removed, cooled and rinsed free of adhering salts. Further treatment of the article is according to conventional methods which form no part of the present invention and will therefore not be further considered.

When the article is transferred from the chloride austenitizing bath to the austempering quench bath, some of the chloride salts physically adhere to the article, are deposited in the quench bath when the article is immersed therein, and go into solution. From this it can be appreciated that with repeated auste'mpering operations with successive steel articles in the same baths, the concentration of chloride salts in the quench bath gradually increases. Since the melting point of the initial nitratenitrite quench bath is in the order of about 300 F., while that of the chlorides is about 1300 F., the chloride content of the quench bath will increase until it reaches its limit of solubility in the nitrate-nitrite bath,-after which additional chlorides will precipitate out and settle to the bottom of the bath or will freeze against colder surfaces within the bath. As it is desirable to maintain the quench bath at about 750 F, it becomes obvious that the bath will become contaminated to the point where it will be completely unsuable and could even freeze at this temperature if the chloride content becomes sufiiciently high. It has been found that the quench bath at 750 F. can tolerate the presence of chloride salts up to about 17% by weight as a maximum concentration. Thus if the chloride content exceeds about 17% by weight, the chlorides precipitate out, forming a sludge in the quench bath. At this point the quench salts are either (1) corm pletely or partly discarded and replaced by fresh nitratenitrite salts or (2) the sludge is manually bailed out by means of a screened shovel which allows the nitratenitrite salts to pass throughbut retains the precipitated chlorides. Because of wetting action, the sludge which 2,931,745 Patented Apr. 5, 1960 is discarded may contain up to 70% nitrate-nitrite salts and only 30% chloride salts. However, such procedure is not desirable because sodium nitrate, potassium nitrate and sodium nitrite salts are much more expensive than the chloride salts which are comparatively cheap. Thus the problem is to remove the chloride salts from the quench bath with minimal loss of nitrate-nitrite salts for main: taining fused condition of the quench bath at its operating temperature, thereby reducing the cost of the austernpering operation.

It is therefore an object of this invention to separate inorganic alkali metal chlorides from a molten alkali nitrate-nitrite salt quench bath.

A further object of this invention is to recover economically a major portion of the sodium nitrate-potassium nitrate-sodium nitrite salts from an austempering and martempering quench bath for re-use in said bath.

'A still further object of this invention is to reclaim economically the sodium nitrate-potassium nitrate-sodium nitrite salts of an austempering and martempering quench bath for re-use in said bath by removing the major portion of chloride salts therefrom.

Another object of this invention is to economically remove suflicient chloride salts from an austempering and martempering quench bath to maintain the freezing temperature of said bath substantially below its desired operating temperature.

Another object is to maintain the chloride content of the quench bath both low and constant so that the quenching power of the bath is stabilized at an efiicient nitratenitrite composition.

. These and other desirable andimportant objectsin herent in and encompassed by the invention will be more readily understood from the ensuing description, the appended claims and the annexed drawings wherein:

Figure 1 is a diagram illustrating schematically the components comprising the apparatus and their respective relationship to the invention.

Figure 2 is a diagram illustrating schematically the components comprising the apparatus and their respective relationship to each other in a modified form of the invention.

As mentioned previously in repeated austempering and martempering operations, by mechanical adherence to the articles being austenitized in the alkali metal chloride bath (not shown), chloride salts are mechanically deposited in the austempering and martempering quench bath 10 (Figure 1), and after a time the build-up of chloride salt content in the bath 10 would reach a concentration such that the bath 10 would no longer remain fluid at the desired quenching temperature. When the chloride content, exceeds its solubility at the operating temperature of the bath, freezing begins on the Walls of the receptacle 11 supporting the bath l0 and progresses inwardly until the bath is'completely sludged over, and/or the excess chlo-i rides are precipitated within the bath 10 and settle to the. bottom of the tank until the bath is completely inoperable for its intended purpose. This can be avoided as follows:v

Referring to Figure 1 there is provided a plate separator pot 12 communicatively connected to the bath 10 by a pipe indicated at 13 on the upper portion thereof. The

lower portion of the bath 10 is communicatively con-, nected to the outlet side of a pump P by a pipe indicated at 14. The inlet side of the pump P is communicatively connected to the pct 12 by the pipe indicated at 15. Thus the pump P functions to circulate the liquid salts of the bath 10 through the pot 12. The tempertaure in; pot 12 is maintained at or above the operating tempera; ture of bath 10. The pot 12 is provided with a remova-I ble separator plate 16 partly immersed therein. The plate 16. is provided with conventional passages (not shown) for circulating a fluid coolant therethrou'gh. The

water therein.

liquid coolant enters the plate 16 at the inlet ports 17 and 17' and is discharged through the outlet ports 18 and 18 as shown in Figure 1. In order to prevent an appreciable temperature reduction of the pot 12 it is preferred that the coolant be adjusted to maintain the plate 16 at about 100 F. below the temperature of pot 12. Thus the plate 16 being about 100 F. cooler than the pot 12 causes the chloride salts to adhere and crystallize out in solid form on the plate 16. When the plate 16 contains an appreciable amount of adhered chloride salts the entire plate 16 is mechanically removed from the pot 12 and partly immersed (to the same extent as that in the pct 12) into a low temperature or quench pot 19 as indicated schematically by the arrow 20. For convenience when the plate 16 is removed from the separator pot 12 to the low temperature or quench pot 19 it is referred to by the numeral 16.

The quench pot 19 contains a liquid solution 22 of about 87% by weight of nitrate-nitrite salts with about water and up to about 3% chloride salts. With reference to chloride salts (potassium chloride and sodium chloride) this composition at 3% chloride salt corresponds to the maximum solubiilty of the chloride salts in such a bath. The quench pot 19 is maintained at a temperature of between 275 F. and 325 F., preferably at about 300 F. In order to provide water to form the above mentioned solution which also serves to control the temperature in the quench pot 19 a water inlet pipe 21 is provided which may or may not extend below the surface of the liquid in the quench pot 19. The water entering the pipe 21 may conveniently be the rinse water obtained when rinsing the quenched article which may contain some nitrate-nitrite salts as well as chlorides. Thus the nitrate-nitrite salts may be recovered in a simultaneous operation.

When the plate 16 is mechanically removed from the pot 12 the salts adhered thereto consists of a sludge containing about 60% chloride salts in solid form and the remainder is essentially liquid nitrate-nitrite salts mechanically occluded with the solid chlorides. As soon as the plate 16 is immersed as 16' in the quench pot 19, the sludge loses its adherence to the plate 16' apparently due to the temperature gradient between the plate and the solution 22 and the increased solubility of the nitrate-nitrite salts in solution 22because of the The chlorides precipitate while solution 22 'ismaintained essentially unchanged by adding water to keep an amount of about 10% water in the bath. Although the chloride precipitate in the quench pot 19 is indicated as settling on the bottom of the quench pot as indicated at 23, what really takes place is that a slurry is formed in the quench pot wherein the liquid phase is solution 22 and the solid phase is a mixture of potassium chloride and sodium chloride. Thus the slurry comprises the solution 22 and the precipitated chloride salts 23. The slurry 22, 23 is drawn from the quench pot 19 into a mechanical separator 24 through the communicating pipe 25 which may be by gravity or a pump (not shown) interposed in the pipe 25. The mechanical separator 24 may comprise a conventional unit such as a filter press or centrifuge. The solids removed by the separator 24 are deposited into the receiver 26 through pipe 27 and comprise mainly chloride salts with whatever small amount of solution 22 which may adhere after mechanical separation and subsequent rinsing processes. The remainder of the solution '22, containing about 87% by weight of nitrate-nitrite salts, 10% water and about 3% chloride salts, discharged from the mechanical separator 24 is deposited either directly or after being reheated to remove the water in theausitempering quench bath 10 through the pipe 28 by means of gravity or a pump (not shown) interposed therein; It also could be 'cast into bars, allowed to freeze, and tlien'added to the bath 10. 1

Replenishment of the solution 22 in the quench'pot 19 is from the water introduced through the pipe 21, and the nitrate-nitrite salts occluded in the adhered chloride salts carried over mechanically from the separator pot 12 to the quench pot 19 on the separator plate 16 and 16. As pointed out previously the salt deposit on the plate 16 consists of about 60% chloride salts and about 40% mechanically occluded liquid nitrate-nitrite salts.

The salts delivered to the receiver 26 containing mostly chloride salts and the balance nitrate-nitrite salts are discarded if it is not practical from an economical point of view to subject this material to a further extraction process.

From the above it has been shown a practical and economical method of reclaiming in excess of of the nitrate-nitrite salts which can be effectively re-cycled back to the austempering quench bath 10.

Figure 2 shows a modified form of the invention wherein the separator plate 16 and 16 and the plate separator pot 12 are eliminated and yet comparable results can be obtained with that described previously. For clarity the components employed in the modified form of the invention which are similar to that of Figure l are designated by like numerals except that each is increased by 100. Thus the alkali nitrate-nitrite salt quench bath is formed by walls 111. The fused salts of the bath 110 flow directly into the low temperature pot 119 by gravity or other suitable means through pipe 129 as illustrated in Figure 2. The low temperature pot 119 contains a liquid solution 122 consisting of about 87% by weight of sodium nitrate-potassium nitrate-sodium nitrite salts, about 10% water and about 3% alkali metal chlorides and is maintained at about 300 F. as before. To assist in cooling and maintaining the liquid 122 at 300 F. temperature as well as keeping the water content at about 10% by weight a water inlet pipe 121 is provided. The discharge end of the pipe 121 may or may not be positioned below the surface of solution 122 in the low temperature pot 119.

As the fiuid salts from the bath 110 enter the pot 119 through the pipe 129 the reduction in temperature from the operating temperature to 300 F., causes the chloride salts which are in excess of their limit of solubility in solution 122 to crystallize out in solid form 123. Although the drawing indicates that the solid chlorides 123 settle at the bottom of the pot 119 what actually happens is that, as before, a slurry is formed. The slurry 122, 123 comprises the solution 122 as the liquid phase and the excess solid chloride salts as the solid phase. The slurry 122, 123 thus formed is drawn off to the mechanical separator 124. Again the mechanical separator may comprise a conventional unit such as a filter press or centrifuge. The solids removed by the separator 124 are deposited into the receiver 126 through pipe 127 and comprise mostly chloride salts with whatever small amount of solution 22 which adheres after mechanical separation and subsequent rinsing processes. The remainder of the solution 122 containing about 87% by weight of nitrate-nitrite salts, 10% water and about 3% chloride salts, discharged from the separator 124 is deposited in the austempering quench bath 10 through the pipe 128 in the same manner as previously described.

In order to recover the nitrate-nitrite salts which physically adhere to the steel articles being processed after the articles are removed from bath 110, the water from the bath (not shown) in which they are rinsed is introduced through inlets 21 or 121 into baths 19 and 119, thus recovering the nitrate-nitrite salts which dissolved in the rinse bath.

Having thus described the preferred embodiments of the invention it can now be seen that the objects of the invention have been fully achieved and it must be understood that changes and modifications may be made which do not depart from the spirit of the invention nor from the scope thereof as defined in the appended claims.

and ,i

What is claimed:

1. For reducing contaminating excess alkali metal chlorides content of a molten austempering and martempering quench bath initially containing salts selected from the group consisting of alkali metal nitrates and alkali metal nitrites, the method of flowing said contaminated molten bath into a low temperature pot, introducing into said pot up to about by weight of water to form a liquid solution with said salts for precipitating excess alkali metal chlorides in solid phase, and mechanically separating said solid phase alkali metal chlorides from said liquid composition.

2. For removing substantially all contaminating alkali metal chlorides in excess of about 3 percent by weight from a molten austempering and martempering quench bath initially containing salts selected from the group consisting of alkali metal nitrates and alkali metal nitrites, the method of transferring at least a portion of said contaminated molten bath into a low temperature pot, introducing into said pot up to about 10% by weight of water to form aliquid phase composition with said salts for precipitating excess alkali metal chlorides in solid phase, mechanically separating said solid phase alkali metal chlorides substantially from said liquid phase composition, and discharging said liquid phase composition into said bath.

3. For removing substantially all contaminating alkali metal chlorides in excess of about 3% by weight from a molten austempering and martempering quench bath initially containing salts selected from the group consisting of alkali metal nitrates and alkali metal nitrites, the method of transferring at least a portion of said contaminated bath into a low temperature pot, adding to said pot sufficient water to form a liquid phase composition with said salts for precipitating excess alkali metal chlorides in solid phase, mechanically separating said solid phase alkali metal chlorides substantially from said liquid phase composition and discharging said liquid phase composition into said bath.

4. For removing substantially all contaminating alkali metal chlorides in excess of about 3% by weight from a molten austempering and martempering quench bath initially containing salts selected from the group consisting of alkali metal nitrates and alkali metal nitrites, the method of transferring at least a portion of said contaminated bath into a low temperature pot, said pot being maintained at a temperature between about 275 F. and about 325 F., introducing into said pot sufiicient water to form a liquid phase composition with said salts for precipitating excess alkali metal chlorides in solid phase, mechanically separating said solid phase alkali metal chlorides substantially from said liquid phase composition 2ndh discharging said liquid phase composition into said 5. For removing substantially all contaminating alkali metal chlorides in excess of about 3% by weight from a molten austempering and martempering quench bath initially containing at least one salt selected from the group consisting of sodium nitrate, potassium nitrate, and sodium nitrite, the method of transferring at least a portion of said contaminated bath into a low temperature pot, said pot being maintained at a temperature of about 300 F., introducing into said pot sufiicient water to form a liquid phase composition consisting of about 10% by weight of water, up to about 3% by weight of alkali metal chlorides and the balance being said nitrogen containing salts for precipitating alkali metal chlorides in excess of said 3% by weight in solid phase, mechanically separating said solid phase alkali metal chlorides substantially from said liquid phase composition and discharging said liquid phase composition into said bath.

6. For reducing contaminating alkali metal chlorides content of a molten austempering and martempering quench bath initially containing at least one salt selected from the group consisting of alkali metal nitrates and alkali metal nitrites, the method comprising theffiowing of said contaminated molten bath into a separator pot, providing a plate, means for maintaining the tempera ture of said plate substantially below the temperature of said bath, providing a low temperature pot, said low temperature pot having a liquid solution comprising of up to about 3 percent by weight alkali metal chlorides with water and at least one salt selected from the group consisting of alkali metal nitrates and alkali metal ni trites, said liquid solution being maintained at a temperature substantially below the temperature of said plate, immersing at least a portion of said plate in said separator pot for inducing at least a part of said chlorides of said bath to precipitate in solid phase on said plate, mechanically removing from said separator pot, said plate with said precipitated chlorides adhered thereto and thereafter immersing at least a portion of said plate with said solid phase chlorides into said liquid solution in said low temperature pot for depositing said solid phase chlorides therein, mechanically extracting said solid phase chlorides from said liquid solution and returning said extracted liquid solution to said austempering and martempering quench bath.

7. For removing substantially all contaminating alkali metal chlorides in excess of about 3 percent by weight from a molten austempering and martempering quench bath initially containing at least one salt selected from the group consisting of alkali metal nitrates and alkali metal nitrites, the method comprising the transferring of said contaminating molten bath into a separator pot,

providing a plate, means for maintaining the temperature of said plate approximately F. below the temperature of said separator pot, providing a low temperature pot, said low temperature pot having a liquid solution comprising of up to about 3% by weight of alkali metal chlorides with about 10% by weight of water and the balance being at least one salt selected from the group consisting of alkali metal nitrates and alkali metal nitrites, said liquid solution being maintained at a temperature of about 75 F., to about 325 F., immersing at least a portion of said plate in said separator pot for inducing at least a part of said chlorides of said bath to precipitate in solid phase on said plate, mechanically removing said plate with said precipitated chlorides adhered thereto and thereafter immersing at least a portion of said plate with said solid phase chloride salts into said liquid solution in said low temperature pot for depositing said solid phase chlorides therein, mechanically extracting said solid chlorides substantially from said liquid solution and returning said extracted liquid solutiOn to said austempering and martempering bath.

8. For removing substantially all contaminating alkali metal chlorides in excess of about 3 percent by weight from a molten austempering and martempering quench bath initially containing at least one salt selected from the group consisting of alkali metal nitrates and alkali metal nitrites, the method comprising the transferring of at least a portion of said contaminated bath into a separator pot, providing a plate, means for maintaining the temperature of said plate approximately 100 F. below the temperature of said separator pot, providing a low temperature pot, said low temperature pot containing a liquid solution comprising of up to about 3 percent by weight of alkali metal chlorides with water and the balance being at least one salt selected from the group consisting of alkali metal nitrates and alkali metal nitrites, means for introducing into and maintaining about 10 percent by weight of water in said liquid solution, said liquid solution being maintained at a temperature of about 275 F., to about 325 F., immersing at least a portion of said plate in said separator pot for inducing at least a part of said chlorides of said bath to precipitate in solid phase on said plate, mechanically removing said plate with said precipitated chlorides adhered thereto and thereafter immersing at least a portion of said turning said extracted liquid solution to said austempering and martempering bath.

9. For removing substantially all contaminating alkali metal chloride salts in excess of about 3 percent by weight from a molten austempering and martempering quench bath initially containing at least one salt selected from the group consisting of sodium nitrate, potassium nitrate, and sodium nitrite, the method comprising the transfer ring of at least a portion of said contaminated bath into a separator pot, providing a plate, means for maintaining the temperature of said plate at approximately 100 F, below the temperature of said pot, providing a low temperature pot, said low temperature pot containing a liquid solution comprising of up to about 3% by weight of alkali metal chlorides with water and the balance being at least one salt selected from the group consisting of sodium nitrate, potassum nitrate, and sodium nitrite, means for introducing into and maintaining about 10 percent by weight of water in said liquid solution, said liquid solution being maintained at a temperature of about 275 F., to about 325 F., immersing at least a portion of said plate in said separator pot for inducing at least a part of said chloride of said bath in excess of about 3 percent by weight to preciptate in solid phase on said plate, mechanically removing said plate withisaid precipitated chlorides adhered thereto and thereafter immersing at least a portion of said plate with said solid phase chloride salts into said liquid solution in said low temperature pot for depositing said solid phase chlorides therein, mechanically extracting said solid chloridessubstantially from said liquid solution and returning said extracted liquid solution to said austempering and martempering bath.

' No references cited. 

2. FOR REMOVING SUBSTANTIALLY ALL CONTAINING ALKALI METAL CHLORIDES IN EXCESS OF ABOUT 3 PERCENT BY WEIGHT FROM A MOLTEN AUSTEMPERING AND MARTEMPERING QUENCE BATH INITALLY CONTAINING SALTS SELECTED FROM THE GROUP CONSISTING OF ALKALI METAL NITRATES AND ALKALI METAL NITRITES, THE METHOD OF TRANSFERRING AT LEAST A PORTION OF SAID CONTAMINATED MOLTEN BATH INTO A LOW TEMPERATURE POT, INTRODUCING INTO SAID POT UP TO ABOUT 10% BY WEIGHT OF WATER TO FORM A LIQUID PHASE COMPOSITION WITH SAID SALTS FRO PRECIPITATING EXCESS ALKALI METAL CHLORIDES IN SOLID PHASE, MECHANICALLY SEPARATING SAID PHASE ALKALI METAL CHLORIDES SUBSTANTIALLY FROM SAID LIQUID PHASE COMPOSITION, AND DISCHARGING SAID LIQUID PHASE COMPOSITION INTO SAID BATH. 